The present invention relates to delivery systems for liquid phosphorous precursors, and in particular to stainless steel containers, piping and injection valves for injecting liquid triethylphosphate (TEPO), TMP or TEP into a chemical vapor deposition (CVD) chamber.
A variety of different systems can be used to deliver processing gases to a chemical vapor reaction chamber. In a boiler system, the liquid is heated into vapor form. In a "bubbler" system, gaseous helium is introduced into a liquid in a container, resulting in some of the liquid being bubbled out of solution. When the liquid contains a phosphorous precursor, such as TEPO, TMP or TEP, and the container or piping is stainless steel, residue build-up has been observed, in particular where the stainless steel is exposed to heat.
Injection valves are often used for providing a processing gas to a CVD chamber. In one method of doing this, the active gas component is provided in liquid form to an injection valve. The injection valve provides the liquid through an orifice past which a carrier gas is provided. A pressure drop is created which causes the liquid to vaporize into gaseous form. Typically, a heater is also provided on the valve to prevent condensation of the processing gas. A typical inert carrier gas is helium.
One problem encountered with such valves is the build-up of residue around the orifice, which can prevent proper seating of a cut-off plug to hinder control of the valve. Excessive build-up of residue can also block the orifice itself, or severely restrict the flow of liquid through the orifice. Residue build-up on other surfaces can contaminate subsequent gases flowing across the surface or contained in the container.
Accordingly, it would be desirable to have an liquid phosphorous precursor delivery system which minimizes the build-up of residue on stainless steel surfaces.